Tag Archives: Docker Linux Containerization

In these series of Docker tutorials, i will walk you through a hands on experimentation with Docker. The operating system I am working on is Ubuntu 16.04.

Docker is a containerization technology which allows deployment of applications in containers. Its advantage is speed, a docker container hosting an application would be up and running in a few milliseconds.

As opposed to Virtual machines, containers run on top of the host OS. They share the host kernel. Thus you can only run a Linux container on a Linux host or machine.

Installation Limitation – Docker runs on 64-bit OS only and it supports Linux kernel version 3.10 and above. You can verify this using the commands below –

root@lindell:~# arch
x86_64
root@lindell:~# uname -r
4.4.0-47-generic

Docker – terminology

Images – are the building blocks of Docker. Once created or built, they can be shared, updated and used to launch containers. No image, no containers.

Containers – are images in action. Containers give images life, containers are image plus all the ecosystem the Operating system need to run the application.

Registry – where images are stored. They can be public or private. DockerHub is a typical example of public registry.

Data volumes – persistent storage used by containers.
Dockerfile – file containing instructions to be read by Docker for building a Docker image.

Node – physical or virtual machine running Docker engine.

Our first Docker container
After installing docker and making sure that the Docker engine is running, run the commands below to check the Docker images(‘docker images’) available or if any Docker containers are running(‘docker ps’). Both commands should not return any results if this is a first time installation.

We just downloaded an official Ubuntu image and started an Ubuntu container by running /bin/bash inside the newly started container. The ‘-ti’ option runs bash interactively(-i) by allocating a pseudo-TTY(-t).

Note that – the kernel version on the container is the same as the host’s kernel version. During first run, Docker will try to find Ubuntu image in our local storage, if it can’t find it, it downloads it from Docker Hub. On next runs, starting the containers will be much faster.

At this point, if we exit from the container, docker ps will no longer show the container as it has been terminated. We use ‘docker ps -a’ instead to view it and then use ‘docker start’ command to start the container –